What is the definition or description of: bundle branch block?

Electrical blocks. There are 2 main branches of the heart's electrical system within the ventricles, the right bundle branch and the left bundle branch. Additionally, the left bundle branch has two sub-branches, the antero-superior fascicle and the posteroinferior fascicle. When one or more branches are disrupted, the resultant electrical abnormalities can be detected on an electrocardiogram.